To Test or Not to Test: Urine Drug Monitoring in Chronic Pain Management

Urine drug testing can be an effective part of opioid treatment when correctly applied and interpreted. However, the evidence supporting the use of urine drug testing in certain circumstances is limited at best, and some studies show that primary care physicians, family physicians, and other clinicians with limited training in pain management may not fully understand the uses, limitations, and potential pitfalls associated with the use of urine drug testing in practice.

Several studies indicate that non-pain specialist primary care physicians may require additional education and training in the proper use of urine drug testing with patients being treated with opioids. In “Family Physicians Proficiency in Urine Drug Test Interpretation,” published in the Nov/Dec 2007 issue of the Journal of Opioid Management (http://hcp.lv/oWiqca), Reisfield, et al. used a multi-choice questionnaire to test family medicine physicians’ knowledge of urine drug testing in the pain management setting and their proficiency in interpreting test results. They found no statistically significant difference in knowledge between physicians who regularly ordered urine drug tests and those who did not. They concluded that “family medicine physicians who order urine drug testing to monitor their patients on chronic opioid therapy are not proficient in their interpretation.” The authors of another study (http://hcp.lv/jOlpcI) found limited use of opioid risk reduction tools in the primary care setting, even for high-risk patients. In the study, although patients with a drug use or mental health disorder were more likely to receive urine drug testing, overall less than 8% of patients received urine drug screening (random or otherwise) as part of their treatment, suggesting that primary care physicians are either unaware of/ uncomfortable with the use of urine drug testing, or are actively forgoing its use for some reason (perhaps because of the dearth of strong evidence in support of it).

Recommendations for use

Still, despite the thin evidence base supporting the use of this monitoring tool, several guidelines recommend the use of urine drug testing as part of opioid therapy for chronic pain. The American Pain Society/American Academy of Pain Medicine “Clinical Guidelines for the Use of Chronic Opioid Therapy in Chronic Noncancer Pain,” published in the February 2009 issue of the Journal of Pain (http:// hcp.lv/lmXhYJ), note that although there is only low-quality evidence to support the effectiveness of using a written opioid treatment plan that “documents patient and clinician responsibilities and expectations,” such a written plan can help “reinforce expectations about the appropriate and safe use of opioids,” especially with patients who may be at higher risk for misuse or abuse of opioid medications. Although there is “insufficient evidence to guide specific recommendations on which provisions to include” in a written treatment agreement plan, sample plans (http://hcp.lv/pkkuAW) may specify that patients must only obtain opioid prescriptions (in limited amounts) from one physician and fill those prescriptions at one designated pharmacy, and require patients to attend regular office visits for follow up that may include pill counts and random urine drug screens.

Nafziger and Bertino, in “Utility and Application of Urine Drug Testing in Chronic Pain Management with Opioids,” published in the January 2009 issue of the Clinical Journal of Pain (http://hcp.lv/qoiId4), offer an useful and succinct summation of the value of urine drug testing as part of a pain management program: Urine drug testing (UDT), “when used with an understanding of the principles of pharmacokinetics, pharmacodynamics, and pharmacogenetics of opioids, can be a useful tool in chronic pain management. Clinicians must keep in mind the limitations, purpose, and value of UDT, and the inability to predict patient compliance with a drug dosage using commercial algorithms.”

Testing can’t tell you everything that your patient has been up to

Differences in the type of drugs and products screened for, the type of test, the quality and accuracy of the test, the ability of the treating physician and/or lab personnel to decipher the results, and other factors come into play when interpreting the results of urine drug testing. And although a test may indicate the presence (or absence) of a particular drug, it won’t necessarily explain why that results came about. Not all urine drug tests are equal— immune-assay drug panels “can vary from one laboratory to another, as can the lower limits of drug detection. No-threshold testing is mentioned in pain management literature, but is not often available in clinical practice.” Clinicians who intend to use these tests in practice should consult with certified laboratory professionals when ordering urine drug tests and interpreting the results and “ask laboratory personnel which drugs are included in their facility’s urine test panel and what the lower limits are” (http://hcp.lv/oMcqlX).

The American Pain Society/American Academy of Pain Medicine guidelines mentioned above reinforce the point that the effective use of urine drug testing requires a thorough understanding of the capabilities and limits of this technology. The authors cautioned that although “the evidence on the accuracy of urine drug screening to identify aberrant drug-related behaviors or diversion is lacking, and no evidence exists that demonstrates that screening improves clinical outcomes, absence of prescribed opioids or presence of unprescribed opioids or illicit drugs can be a marker for problematic issues that would not be apparent without urine drug screening. Interpretation of urine drug screen results is a challenge, and requires an understanding of opioid drug metabolism, pharmacokinetics and limits of laboratory testing methods. In fact, urine drug screen results usually do not suggest a definitive course of action, but rather should be interpreted in the context of individual patient circumstances” (http://hcp.lv/lmXhYJ).

Cone and Kaplan, in the July 2009 issue of Postgraduate Medicine (http://hcp.lv/pw44jR), concluded that although urine drug tests can detect prescribed and illicit substances that are present above a specific threshold, they only provide “limited data about the source, dose, or route of administration of substances detected. Effective monitoring requires careful test selection, an understanding of pharmacologic and metabolic factors influencing test results, and awareness of methods by which patients who are substance abusers may tamper with test specimens to escape detection… Given its inherent complexities, effective urine testing requires close collaboration between the primary care physician and a reliable laboratory to develop an appropriate test protocol for each patient and to interpret test results.”

Does a positive have to be a negative?

Stewart Leavitt, MA, PhD, author of the terrific Pain-Topics.org (and member of this magazine’s editorial advisory board) has compiled a list of considerations and cautions that attend the use of urine drug testing in clinical practice, some of which may not be common knowledge:

• Morphine preparation often contain impurities, including low levels of codeine, that may be detected by some tests (this is also true for hydrocodone, which may be present as an impurity in some oxycodone and thus may show up in test results for patients who have been presecribed high doses of this drug).
• Patients may have genetic variants in the CYP450 enzymes in the liver that may alter the metabolism of some opioids, resulting in the unexpected presence or absence of these drugs in test results.
• “Unanticipated conversions between opioids going beyond common metabolic pathways may occur” in some patients, potentially leading to false and damaging test results.

You can read the complete list (as well as Leavitt’s valuable insights into the “pitfalls of urine drug monitoring in pain care”) at the Pain-Topics.org website (http://hcp.lv/pVBm1s).